Solid-state cameras are capable of acquiring high quality images due to their good energy resolution and their high spatial resolution. The energy resolution is mainly dependent on the intrinsic physical properties of the materials from which the detectors of the camera head are made. Such materials are generally various types of semiconductors, such as, CdTe, CdZnTe, Si, GaAs, Ge, InGaAs, and AlGaAs. On the other hand, the spatial resolution of solid-state cameras is mainly dependent on the geometrical design and the dimensions of the pixels that form the focal-plane arrays of the detectors in the camera heads. In the field of X-ray and Gamma ray imaging, the spatial resolution is dictated by the convolution between the resolution of the pixels in the detector focal plane and the resolution of the collimator that is generally placed in front of this focal plane.
In order to produce a high quality image, the detector must be capable of achieving high energy resolution, high spatial resolution, and high sensitivity, which provides good contrast. In addition the spatial transformation from the object plane to the focal plane array should be done accurately. In order to produce this transformation accurately and without image deformation, the pitch between the pixels in the focal-plane of the detectors of the camera head should be maintained constant over the whole of this plane.
A technology known as Z-technology, whose development started in the early 1970's, enables the production of a focal plane array of any desired size by butting individual pixelated detector modules from all their sides. Z-technology is described in a recent review article entitled “Applications of Advanced Z-Technology Focal Plane Architectures” by J. C. Carson, published in SPIE Vol. 930, Infrared Detectors and Arrays, pp. 164-182 (1988), and variously in U.S. Pat. Nos. 4,490,626, 4,525,921, 4,551,629 and 4,555,623, all of which are hereby incorporated by reference, each in its entirety. This butting capability is achieved by integrating all the read-out electronics coupled to each of the detector pixels, on the back side of the detector and in a form of stacks of layers in the Z-direction, the detector plane being oriented in the X-Y plane. This configuration, with the electronic read-outs in the Z-direction, leaves the module sides free to be butted with their neighbors and with surrounding modules.
In this technique, each module includes an integral number of pixels, set apart from each other by the pixel pitch. To maintain this pitch over the whole of the focal plane, which is required for obtaining an accurate image, individual modules must be butted with no dead spaces between them, and at a fixed pitch between module and module. Butting of the modules with no spaces between them also assures that there will be no dead areas in the camera head, which do not contribute to image acquisition.
However, normal production techniques are such that the module dimensional tolerances, and those of the assembly components by means of which they are mounted onto the electronic base board in the camera head, may result in either unacceptable gaps between neighboring modules, or conversely, interference between the adjacent edges of the modules, such that they cannot even be fitted into the base board side-by-side. Even if all the modules could be fitted into the array, the periodicity of the pixel pitch would be degraded because of these tolerances. Production of the modules with such tight tolerances that they would all fit together “perfectly” would make the cost of such a camera head prohibitive.
There therefore exists a need for a method of constructing and arranging detector modules, which can be tiled to produce focal-plane arrays of pixelated detectors having constant pitch, such that, in spite of generally used production tolerances for these modules, they can be mounted in a continuous and regular tiled pattern on a Detector Carrier Board (DCB). Furthermore, the need exists that in such a focal-plane arrays of detector modules, the modules can be freely removed from and inserted into the DCB, while still maintaining constant pitch of the pixels over the whole focal-plane of the cameras.
The disclosures of each of the publications mentioned in this section and in other sections of the specification are hereby incorporated by reference, each in its entirety.